In 1995, Professor Hosono proposed transparent amorphous oxide semiconductors (TAOS)(Note 2) with high electronic mobilities. Since then, as leader of JST ERATO and ERATO-SORST projects, Professor Hosono made TFTs at room temperature using one kind of TAOS, IGZO (indium-gallium-zinc oxide)(Note 3). Because their electronic mobilities are 10 to 20 times those of amorphous silicon(Note 4), displays made with IGZO TFTs can have 10 times better resolution. Being easily made on plastic films at lower temperatures than current materials, IGZO TFTs should find a broader range of applications. Spurred by this and beginning with Samsung, several display makers both inside and outside Japan developed prototype high resolution, 3D and large area LCD and OLED displays using IGZO TFTs.

This agreement with a world leading display maker will advance application to high resolution, 3D and large area LCD displays, and will accelerate developments for IGZO TFTs in smaller displays for smart phones and tablet devices, and for electronic paper. So JST expects similar efforts by other display makers. These basic research results from Japan are expected to have major impact on the 10 trillion yen global display industry.

The research results upon which this license is based arose from the following projects and research areas.

Taking advantage of nanostructure present in the crystal structures of oxides and related compounds, Professor Hosono and coworkers generated many results, including “Invention of IGZO TFT,” “Discovery of electrically conducting cement 12CaO-7Al2O3,” and “Discovery of iron-based high temperature superconductors.”

<Background>

Information from televisions, computers and mobile phones is essential to modern society. The flat panel displays that transmit this information contain TFTs that operate by switching electricity on and off.

Currently, TFTs are made with amorphous silicon hydride (usually called amorphous silicon). However, the high resolution displays of the future demand TFTs with high electron mobility are hard to obtain with this semiconductor, so their development has awaited the creation of new materials.

<Content of Research>

In 1995, Professor Hosono proposed a new material TAOS at the “16th International Conference on Amorphous Semiconductors” held in Kobe. But this received little attention from international peers.

Nonetheless, in 1999, Professor Hosono was selected as a project leader for a JST ERATO project and began research to prove the validity of his proposal. In 2004, He discovered that IGZO, a kind of TAOS, can be easily coated onto plastic film using low temperature vacuum sputtering (Note 5). A patent application was filed in March of that year and a paper published in Nature in November.

<Impact on Industry>

Upon learning of this invention, display makers both inside and outside Japan began applied research. Starting from 2009 in particular, prototypes and exhibits of high resolution, 3D and large area liquid crystal displays and organic electroluminescent displays became prominent at international conferences and exhibitions. The current licensing partner, Samsung Electronics Co., Ltd., began applied research early and surprised the global panel industry at Flat Panel Display International 2010 held at Makuhari in November 2010 with a high resolution (3840 x 2160 pixels), 3D (screen refresh rate 240 Hz), 70-inch liquid crystal display, and are expected to commercialize it early on.

<Future Development>

JST expects to further license patents related to IGZO TFT technology to other domestic and foreign display makers.

Professor Hosono comments, “Believing that materials are there to be used, I held from the beginning that licenses are to be granted domestically and internationally to strongly interested parties without discrimination. It is a fundamental wish of material scientists for the results of basic research in universities to manifest themselves as products that can be seen.” As needs increase in the displays industry, we can expect much from the industrial introduction of IGZO TFTs that are a result of Japanese basic research and development.

Figure 1. The “IGZO TFT” discovered in 2004 by Professor Hosono.

Professor Hosono demonstrated that thin films of IGZO can be made on plastic film by low temperature sputtering and that their TFT performance (electron mobility) is 10 to 20 times that of amorphous silicon.

<Glossary>

Note 1: Thin film transistor (TFT)

Transistors are essential to modern electronic devices and are semiconductor elements that amplify or switch electrical signals in electronic circuits. A TFT is a thin transistor that is formed on a substrate. In liquid crystal displays, each of the dots that make up the screen is controlled by a TFT.

Note 2: Transparent amorphous oxide semiconductors (TAOS)

It is common knowledge that the ease with which electrons move (electron mobility) is orders of magnitude lower for amorphous semiconductors, in which atom arrays are disordered, than in crystal semiconductors, in which atoms are regularly ordered. For example, electron mobility is three orders of magnitude less for amorphous silicon than for crystalline silicon. Nonetheless, in 1995, Professor Hosono proposed amorphous oxide semiconductors that show little loss of mobility because the electron orbitals of their heavy metal ions and oxygen ions spatially spread symmetrically. He named this group of substances “transparent amorphous oxide semiconductors.” They are as transparent as glass, electrons move as easily as in crystals, and semiconductors can be made in which electric current can be controlled.

Note 3: IGZO

Pronounced “igzoe”, IGZO is an abbreviation for amorphous oxides made from the elements indium (In), gallium (Ga) and zinc (Zn), and is one of the TAOS substances proposed by Professor Hosono. Its electron mobility is 10 to 20 times that of amorphous silicon and thin films can be made that are transparent to visible light. Films can be made by low temperature sputtering without having to heat the substrate. This opens up a broad range of applications because films can be made on plastic films and other materials that are sensitive to high temperatures.

Note 4: Amorphous silicon

In 1975, British scientists Walter Spear (deceased) and Peter LeComber discovered a process for making amorphous semiconductors of silicon containing hydrogen by decomposing silane (SiH4) in a glow discharge. Its electron mobility is markedly less than single crystal silicon but it has become the mainstay of the TFTs that drive liquid crystal displays and solar batteries because it is easy to form uniform thin films over large areas.

Note 5: Sputtering

Sputtering is a method for forming thin films of a target material on substrates. In this method, the target (IGZO that will form the film) and substrate are placed in a vacuum with inert gas (mainly argon) and a high DC voltage applied between the target and substrate. Ionized argon bombards the target, knocking off material that is deposited on the substrate to form a thin film.

JST, an integrated organization of science and technology in Japan, establishes an infrastructure for the entire process from the creation of knowledge to the return to the society. For more information, visit http://www.jst.go.jp/EN/